During the next year our primary research objectives will be: 1) Continue our studies on the nucleotides capable of initiation of particular mRNA for T4-specific enzymes. Particular attention will be given to the mRNA for deoxynucleotide kinase. 2) We have devised a method for labeling the active site of glutamine for the enzyme, Formylglycinamide ribonucleotide (FGAR) amidotransferase with C14 labeled iodoacetate. Our recent finding that one-half of label attached initially to the enzyme may be released by treatment with alkali represents an important breakthrough in the project. We will identify the released material and also continue to sequence the tryptic peptide containing the stably bound label from C14 labeled iodoacetate. 3) We are initiating a new program with the objective of separating and identifying serum factors required for the initiation of DNA synthesis and cell division of resting cells in tissue culture. Particular attention will be paid in this project to the role of proteases in serum, specifically thrombin and prothrombin.